The International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) Moving Picture Experts Group-4 (MPEG-4) Part 10 Advanced Video Coding (AVC) standard/International Telecommunication Union, Telecommunication Sector (ITU-T) H.264 Recommendation (hereinafter the “MPEG-4 AVC Standard”) is the first video coding standard that employs spatial directional prediction for intra coding. The MPEG-4 AVC Standard provides a more flexible prediction framework such that the coding efficiency is greatly improved over previous standards in which intra prediction was performed only in the transform domain. In the MPEG-4 AVC Standard, spatial intra prediction is performed using the surrounding available samples, which are the previously reconstructed samples available at the decoder within the same slice. For luma samples, intra prediction can be performed on a 4×4 block basis (denoted as Intra—4×4), an 8×8 block basis (denoted as Intra—8×8), and a 16×16 macroblock basis (denoted as Intra—16×16). Turning to FIG. 1A, MPEG-4 AVC Standard directional intra prediction with respect to a 4×4 block basis (Intra—4×4) is indicated generally by the reference numeral 100. Prediction directions are generally indicated by the reference numeral 110, image blocks are generally indicated by the reference numeral 120, and a current block is indicated by the reference numeral 130. In addition to luma prediction, a separate chroma prediction is conducted. There are a total of nine prediction modes for Intra—4×4 and Intra—8×8, four modes for Intra—16×16, and four modes for the chroma component. The encoder typically selects the prediction mode that minimizes the difference between the prediction and original block to be coded. A further intra coding mode, denoted I_PCM, allows the encoder to simply bypass the prediction and transform coding processes. The intra coding mode I_PCM allows the encoder to precisely represent the values of the samples and place an absolute limit on the number of bits that may be included in a coded macroblock without constraining decoded image quality.
Turning to FIG. 2, an exemplary labeling of prediction samples for Intra—4×4 in the MPEG-4 AVC Standard is indicated generally by the reference numeral 200. In FIG. 2, the samples above and to the left of the current block (labeled with letters, from A to M) have been previously coded and reconstructed and, thus, they are available at the encoder and decoder to form the prediction.
Turning to FIGS. 3B-J, Intra—4×4 luma prediction modes of the MPEG-4 AVC Standard are indicated generally by the reference numeral 300. The samples a, b, c, . . . , p of the prediction block are calculated based on the samples A-M using the Intra—4×4 luma prediction modes 300. The arrows in FIGS. 3B-J indicate the direction of prediction for each of the Intra—4×4 modes 300. The Intra—4×4 luma prediction modes 300 include modes 0-8, with mode 0 (FIG. 3B, indicated by reference numeral 310) corresponding to a vertical prediction mode, mode 1 (FIG. 3C, indicated by reference numeral 311) corresponding to a horizontal prediction mode, mode 2 (FIG. 3D, indicated by reference numeral 312) corresponding to a DC mode, mode 3 (FIG. 3E, indicated by reference numeral 313) corresponding to a diagonal down-left mode, mode 4 (FIG. 3F, indicated by reference numeral 314) corresponding to a diagonal down-right mode, mode 5 (FIG. 3G, indicated by reference numeral 315) corresponding to a vertical-right mode, mode 6 (FIG. 3H, indicated by reference numeral 316) corresponding to a horizontal-down mode, mode 7 (FIG. 3I, indicated by reference numeral 317) corresponding to a vertical-left mode, and mode 8 (FIG. 3J, indicated by reference numeral 318) corresponding to a horizontal-up mode. FIG. 3A shows the general prediction directions 330 corresponding to each of the Intra—4×4 modes 300. In modes 3-8 (corresponding to FIGS. 3E-J), the predicted samples are formed from a weighted average of the prediction samples A-M. In DC mode corresponding to FIG. 3D, the predicted samples are the mean of the prediction samples A to D and I to L. Intra—8×8 uses basically the same concepts as the 4×4 predictions, but with a block size of 8×8 and with low-pass filtering of the predictors to improve prediction performance.
Turning to FIGS. 4A-D, four Intra—16×16 modes corresponding to the MPEG-4 AVC Standard are indicated generally by the reference numeral 400. The four Intra—16×16 modes 400 includes modes 0-3, with mode 0 (FIG. 4A, indicated by reference numeral 410) corresponding to a vertical prediction mode, mode 1 (FIG. 4B, indicated by reference numeral 411) corresponding to a horizontal prediction mode, mode 2 (FIG. 4C, indicated by reference numeral 412) corresponding to a DC prediction mode, and mode 3 (FIG. 4D, indicated by reference numeral 413) corresponding to a plane prediction mode. Each 8×8 chroma component of an intra coded macroblock is predicted from previously encoded chroma samples above and/or to the left. Both chroma components use the same prediction mode. The four prediction modes are very similar to the Intra—16×16, except that the numbering of the modes is different. The modes are DC (mode 0), horizontal (mode 1), vertical (mode 2) and plane (mode 3).